The plasma intercooler was a starship system used to provide plasma coolant to the warp drive and other critical systems.
A failure of a plasma intercooler will cause the warp drive to overheat or possibly fail to operate altogether. (TNG: "Relics")
Chief Miles O'Brien took the safeties of the USS Defiant's plasma intercooler offline and never had any problems. Ensign Nog later did the same on the USS Valiant in 2374. (DS9: "Valiant")
Though never stated in canon, "plasma intercooler" may be the proper name of the "intercooler" mentioned in Star Trek: The Motion Picture.